Forming metals

ABSTRACT

A method of producing a metal article, for example a pressure vessel, including the steps of forming an inflatable envelope of a super-plastic metallic alloy, heating the envelope to within the temperature range for super-plasticity, and applying a differential pressure between the interior and the exterior of the envelope such that the envelope expands as a balloon.

United States Patent 1191 Summers et al.

[451 July 22, 1975 FORMING METALS [75] Inventors: Leo Ewart Arthur Summers; John Fyfe Le Cornu-Rickard; David Sidney Underhill, all of Bristol, England [73] Assignee: British Aircraft Corporation Limited, London, England [22] Filed: Jan. 15, 1973 [21] Appl. No.: 323,702

[30] Foreign Application Priority Data Jan. 18, 1972 United Kingdom 2274/72 [52] US. Cl 228/157; 29/421 R; 72/54; 72/D1G. 23; 228/173; 228/263 [51] Int. Cl. B23k 3/02 [58] Field of Search 29/l57.1 R, 475, 480, 481, 29/421; 72/54 [56] References Cited UNITED STATES PATENTS 2,579,646 12/1951 Branson 29/421 2,715,377 8/1955 Gary, Jr. 29/421 X 3,460,224 8/1969 Combes (it al. 29/l57.l R 3,623,204 11/1971 Wagle 3,633,264 l/l972 Gripshover 29/421 OTHER PUBLICATIONS Hayden, H. W., et al., Superplastic Metals, March, 1969, Scientific American, Vol. 220, No. 3, pp. 2835.

Jovane, F., Superplasticity in Titanium, in The Science, Technology, and Application of Titanium, .Iaffee and Promisel, Editors, 1966, pp. 615-623.

Primary Examiner-Francis S. Husar Attorney, Agent, or Firm-Cushman, Darby & Cushman [57] ABSTRACT A method of producing a metal article, for example a pressure vessel, including the steps of forming an inflatable envelope of a super-plastic metallic alloy, heating the envelope to within the temperature range for super-plasticity, and applying a differential pressure between the interior and the exterior of the envelope such that the envelope expands as a balloon.

9 Claims, 5 Drawing Figures FORMING METALS There is a class of metallic alloys which have a composition and microstructure such that, when heated to within an appropriate range of temperatureand when deformed within an appropriate range of strain rate, they exhibit the flow characteristics of a viscous fluid. Such alloys have characteristics indicated by the formula.

where:

m is numerically of the order of 0.7 to 1.00,

f is applied stress (load per unit area), his a constant,

sis strain rate (extension per unit of original length per unit of time), and,

m is the strain rate sensitivity.

The condition in which these characteristics are attained is known as super-plasticity and large deformations are possible without fracture. The present invention is concerned with the working of metals when in this condition.

The invention may be used to provide a method of producing pressure vessels.

Where metal pressure vessels are required to be of light weight, the metal of which they are formed is often difficult to work and accordingly the components of the vessel are often machined from solid billets. One objective of the present invention is to provide a relatively simple and quick alternative method to such machining in the production of pressure vessels. It will be appreciated, however, that the invention is not limited to the production of pressure vessels but has uses in the production of metal articles in general.

According to the present invention a method of producing a metal article includes the steps of forming an inflatable envelope of a metallic alloy of the class hereinbefore described, heating the envelope to within the temperature range for super-plasticity of the metallic alloy, and applying a differential pressure between the interior and the exterior of the envelope such that the envelope expands as a balloon.

Subsequently the envelope is allowed to cool. Preferably the inflatable envelope is formed by metallurgically bonding two layers of the metallic alloy together by means of a welding or, alternatively, a diffusion bonding process. Where a welding process is used, it is preferably of the electron beam type.

The differential pressure is preferably applied to the envelope by admitting a pressure fluid to the interior thereof.

One preferred method according to the invention is now described with reference to the accompanying drawings.

In these drawings:

FIG. 1 is a perspective view of the components of a pressure vessel in an unassembled state,

FIG. 2 is a similar view of the components when assembled prior to forming,

FIG. 3 is a side elevation of a pressure vessel subsequent to forming,

FIG. 4 is an enlarged part-sectional view of the region included in plane IVIV-IV-IV of FIG. 2, and

FIG. 5 is an enlarged part-sectional view of the sectioned area of FIG. 3 shown generally by Arrow V.

The Figures are not to scale.

Referring to the Figures, these illustrate the production of a spherical or near spherical container suitable for use as a pressure vessel. Although a spherical container is illustrated, it will be appreciated that other container shapes can be produced by the method of the invention by changing the shapes of the component parts.

As illustrated, two discs 1 and 2 are cut from a sheet of an alloy containing about 6% aluminium, 4% vanadium, and titanium with a microstructure such that it has super-plastic characteristics. One disc 2 is provided with a small aperture 3 over which is welded a pipe union 4 as shown in FIG. 2. The two discs are placed one on top of the other and are electron beam welded together around their common peripery to form an inflatable envelope. The electron beam is directed radially onto the periphery so that in cross-section the metallurgically bonded area is as shown in FIG. 4. The local area where fusion has taken place is shown at 5.

A source of inert gas is connected by means of a pipe 6 to the union 4 in readiness to pressurise the interior of the envelope. The pressure of the gas admitted to the interior is arranged to be variable up to a maximum of about 200 p.s.i.

The envelope is then placed in an oven and heated to within the range 930950C and then the pressure fluid is admitted initially at a relatively low pressure, say 50 p.s.i. The envelope inflates gradually and, as it does so, the pressure is increased, to say p.s.i. The rate of such inflation is such that it is within the allowable strain rate range for the material of the envelope to retain its super-plasticity so that a spherically or near-spherically shaped vessel is formed as illustrated in FIG. 3. FIG. 5 shows how the weld area deforms during the inflation process; as is evident, the edges of the discs 1 and 2 tend to hinge about the weld fusion area 5 to lie generally in line with one another.

When a desired size of vessel is obtained, the pressure is then reduced to atmospheric and the inflated vessel is then allowed to cool. Should extra strength be required in the region of the weld fusion area 5, the vessel is again welded in this area by the same or another suitable process. An improved joint is thus provided.

To obtain local variations in the shape of the com pleted pressure vessel, the envelope is expanded to contact a mould so that expansion is restricted in a desired locality.

Where ducts are required on the surface of the vessel, to provide a heat exchanger for example, these are produced by metallurgically bonding the edges 7 of strips 8 to the envelope. This is shown in FIG. 3. The strips are of similar material to the envelope and can be attached to the envelope at the same time as the discs 1 and 2 are joined. On heating to within the superplasticity range, the volume between the strip 8 and the envelope is pressurised simultaneously with pressurisation of the envelope, so that the strips inflate to bulge away from the envelope.

Pressure vessels produced in the manner described are capable of withstanding considerable pressure differentials and are of relatively light weight. Moreover they are relatively simply and quickly produced.

We claim:

1. A method of producing a hollow metal vessel, including the steps of:

forming two similar substantially flat sheet members of a super-plastic metallic alloy having a composition and microstructure such that, when heated to within an appropriate temperature range and where deformed within an appropriate range of strain rate, it exhibits the flow characteristics of a viscous fluid;

placing the sheet members in contiguous face-to-face relationship with each other and with their peripheries in register;

forming an inflatable envelope by joining their peripheries together by means of a metallurgical bonding process which provides a peripheral bonded region; heating the envelope to within the temperature range for super-plasticity of the metallic alloy; and

applying a differential pressure between the interior and the exterior of the envelope such that, as it expands as a balloon, the peripheries of the sheet members tend to hinge about the peripheral bonded region to lie generally in line with one another.

2. A method according to claim 1 wherein the sheet members are in the form of discs and the hollow metal vessel is finally of at least nearly spherical form.

3. A method according to claim 1 wherein the sheet members are metallurgically bonded by a welding process which forms a weld fusion area.

4. A method according to claim 1 in which the application of differential pressure is effected by introducing a pressurized inert gas into the envelope.

5. A method according to claim 3 wherein, subsequently to expanding the envelope, the weld fusion area is subjected to further welding process.

6. A method for producing a metal article comprisplacing a pair of generally flat sheets of metallic material in contiguous face-to-face relationship with each other and in superposition so that their borders are substantially in registery;

securing the two sheets together at the borders;

opening a communication to the region enclosed by the sheets;

heating the sheets to such an extent that they behave as super-plastic material;

applying pressure through the communication to said region to inflate the region and thus deflect the sheets away from one another right to the borders thereof without disconnecting the securement at the borders; and

permitting the resulting product to cool and the pressure to return to ambient.

7. The method of claim 6 wherein:

the securing step is performed by forming a fillet weld joining the outer edges of the two sheets along the borders thereof; and

in the pressure applying step, the region is inflated to such an extent that the two sheets, adjacent the borders, each rotate away from their initial position through about so that the two sheets, adjacent the borders and the fillet weld become generally coplanar as seen in radial section.

8. The method of claim 7 wherein the sheets are made of an alloy consisting essentially of:

Constituent Weight Percent Ti 90 Al 6 -Continued Constituent Weight Percent order to modify the shape of the product produced. 

1. A method of producing a hollow metal vessel, including the steps of: forming two similar substantially flat sheet members of a super-plastic metallic alloy having a composition and microstructure such that, when heated to withiN an appropriate temperature range and where deformed within an appropriate range of strain rate, it exhibits the flow characteristics of a viscous fluid; placing the sheet members in contiguous face-to-face relationship with each other and with their peripheries in register; forming an inflatable envelope by joining their peripheries together by means of a metallurgical bonding process which provides a peripheral bonded region; heating the envelope to within the temperature range for super-plasticity of the metallic alloy; and applying a differential pressure between the interior and the exterior of the envelope such that, as it expands as a balloon, the peripheries of the sheet members tend to hinge about the peripheral bonded region to lie generally in line with one another.
 2. A method according to claim 1 wherein the sheet members are in the form of discs and the hollow metal vessel is finally of at least nearly spherical form.
 3. A method according to claim 1 wherein the sheet members are metallurgically bonded by a welding process which forms a weld fusion area.
 4. A method according to claim 1 in which the application of differential pressure is effected by introducing a pressurized inert gas into the envelope.
 5. A method according to claim 3 wherein, subsequently to expanding the envelope, the weld fusion area is subjected to further welding process.
 6. A method for producing a metal article comprising: placing a pair of generally flat sheets of metallic material in contiguous face-to-face relationship with each other and in superposition so that their borders are substantially in registery; securing the two sheets together at the borders; opening a communication to the region enclosed by the sheets; heating the sheets to such an extent that they behave as superplastic material; applying pressure through the communication to said region to inflate the region and thus deflect the sheets away from one another right to the borders thereof without disconnecting the securement at the borders; and permitting the resulting product to cool and the pressure to return to ambient.
 7. The method of claim 6 wherein: the securing step is performed by forming a fillet weld joining the outer edges of the two sheets along the borders thereof; and in the pressure applying step, the region is inflated to such an extent that the two sheets, adjacent the borders, each rotate away from their initial position through about 90*, so that the two sheets, adjacent the borders and the fillet weld become generally coplanar as seen in radial section.
 8. The method of claim 7 wherein the sheets are made of an alloy consisting essentially of:
 9. The method of claim 6 further including: positioning a mould adjacent at least one of the sheets before the inflating has been completed, and, during the inflating, causing the at least one sheet to bulge into engagement with the mould, in order to modify the shape of the product produced. 